The present invention relate to the surface treatment of nuclear fuel assembly components such as fuel rod cladding and control rod guide tubes.
U.S. Pat. No. 4,724,016 (Anthony) discloses the use of ion implantation, particularly N, to enhance the wear and/or corrosion resistance of a zirconium alloy fuel rod cladding. The implantation process should be carried out without depositing a superstrate, i.e., plating surface, that dimensionally alters the component.
Ion implantation has traditionally been performed by the use of an implanter system consisting of an ion source, ion accelerator, mass separation system, and target chamber. Conrad and Forest have developed an alternate process called plasma source ion implantation (PSII) that is useful for semiconductor processing and surface modification of materials. J. R. Conrad et al, IEEE International Conference on Plasma Science, Saskatoon, Canada, May 19-21, 1986. PSII involves immersing the object to be implanted into a steady-state gaseous plasma and repetitively pulse biasing the object to a high negative voltage, thereby accelerating the ions across the sheath and implanting them into the target. PSII is unsuitable for the plating-free implantation of metal ions due to the collection of low-energy ions, and therefore plating of the substrate between bias pulses.
Godechot and Yu developed a surface-modification technique in which metal ion guns were used for simultaneous low-energy ion deposition and high-energy ion implantation. I. G. Brown et al, Applied Physics Letters 58, 1392 (1991). The process described by them is designed to avoid the possibility of plating since the plasma pulse contains no neutral atoms or macroparticles and the substrate is always biased so that there is no low-energy streaming plasma; therefore, the size and geometry of the substance is preserved. Utilizing this process, silicon wafers have been implanted with aluminium ions at doses of up to 3.times.10.sup.14 /cm.sup.2, but the process is energy intensive.
Chan, Meassick and Sroda have recently reported the use of a cathodic arc with electromagnetic dust filter as a source of highly energetic metal ions. The ions are then used for plating-free metal-ion implantation. C. Chan et al, "Plating-free Metal Ion Implantation Utilizing the Cathodic Vacuum Arc As An Ion Source", Appl. Phy. Lett., Vol. 60., No. 2 (March 1992).